According to the Marine Mammal Center, it's at least the fourth dead whale found in the bay so far this year.
VIDEO: Dead whale found lodged under bridge in Oakland estuary
"This is the first time I've ever seen something that," said Sylvester Silva as he and his dad cast their fishing lines not for from the animal. "My Dad and I came out here to do some morning fishing. We get here, see this dead whale right here. It's kind of sad when you really think about it, but it's interesting at the same time."
The whale, all 30 plus feet of it, was stuck underneath a bridge near the Jack London Aquatic Center. It's a body of water that flows into Lake Merritt.
VIDEO: Humphrey the whale leaps into hearts of Bay Area residents in 1985
While construction workers took pictures from above, others came to the shoreline to see for themselves.
"We drove farther down but we couldn't see it," said Alameda's Amy Rose. "So we hopped on our sailboat and came over and finally saw it."
The whale had visible bruising and an open wound on its side. It's not clear if it's the same animal spotted on the bow of a ship entering San Francisco Bay earlier this week.
VIDEO: A look back at the exploding whale of Florence, Oregon
By mid-afternoon, a commercial diving operation arrived, contracted with the Marine Mammal Center, to begin the process of removing the animal from the estuary.
A lone diver went in and tied ropes around the mammoth creature before it was towed away by the barge.
"It's kind of amazing that an animal gets that big," said Tim Pofahl, a tourist from Minnesota. "I've never seen a whale this close. Got to take the opportunity when you can."
RELATED: Dead whale washes up on Angel Island in San Francisco
"It's super sad and also kind of smelly," said Sarah Pofahl.
According to the Marine Mammal Center, the plan is to tow it to Angel Island where a necropsy will be performed in the coming days to determine exact species, age and the cause of death.
Click here for a look at more stories and videos about whales.
Just some of the folks who came down to see the whale found dead near Jack London Square today. pic.twitter.com/PNXKbThiH5— Laura Anthony (@LauraAnthony7) May 18, 2018